1. Field of the Invention
The present invention relates to processes for the extraction of a highly pure material heretofore available in low purity levels and known as glucose tolerance factor (GTF).
2. Discussion of the Background
The importance of dietary chromium and its function in biological systems is long-established. Chromium is an essential trace metal which has been suggested to have an importance role in normal glucose homeostasis. Deficiency of chromium, or of its biologically active form, has been implicated in the pathogenesis of some forms of glucose intolerance and diabetes mellitus.
Beginning in 1957, various investigators have sought to purify from natural sources, or synthesize, a chromium-containing material called GTF, believed to be the biologically active form of chromium. At best only partially purified materials (5 to 10% wt. pure as measured by analysis of sample chromium content) were obtained from natural sources. Synthetic efforts failed to yield GTF.
GTF is reported to be a naturally occurring low molecular weight (600-1000 dalton) organic compound which is water soluble and stable against wet heat, acid, and alkyl treatments. Various investigators have reported that GTF is a complex of nicotinic acid, amino acid components, and Cr.sup.+3. Glycine, cysteine, and glutamic acid have been reported as appearing to be the amino acid components. See, Mooradian et al, Am. J. Clin. Nutr., (1987), 45:877-895.
Toepfer et al, J. Agric. Food Chem., (1977) 25(1):162-166 report that when Brewer's yeast is extracted with dilute alcohol and purified by ion exchange chromatography a product is obtained which possesses GTF activity. This material is reported to contain chromium, nicotinic acid, glycine, glutamic acid, and cysteine.
Toepfer et al also report that when 1 equivalent of trivalent chromium, Cr(Ac).sub.3.H.sub.2 O, is reacted with 2 equivalents of nicotinic acid, 2 equivalents of glycine, 1 equivalent of glutamic acid and 1 equivalent of cysteine a mixture of chromium complexes exhibiting GTF properties are obtained. These materials are however reported to be unstable, precipitating near neutral pH with resulting loss of biological activity.
Although various attempts have been made to isolate a purified form of the GTF product from natural sources and various attempts have been made to produce this material using synthetic methods, obtaining a purified GTF product has so far eluded investigators. In light of the importance of dietary chromium and problems associated with chromium deficiency, such as, e.g., insulin resistant diabetes, there is a strongly felt need for a method for readily obtaining a purified GTF, or a material possessing the biological activity of GTF, in substantial quantities.